Structural elements of music: harmony
Harmony is the set of rules and practices that govern the use of chords.
Chords are groups of sounds at a definite pitch emitted simultaneously. Normally the guitar and the piano are considered the most suitable instruments to play chords, however the electric bass, again departing from its main role, can play them as if it were a guitar (not is it not indeed also called bass guitar?).
Chords are usually organized in sequences commonly called chord progressions, or sequences of two or more chords. A very nice way of playing chords is that of arpeggio (broken chords). Making arpeggio means, playing the notes of the chord, as on a harp, one after the other, hence in melodic form leaving them, however, possibly, resonate together.
So far we have understood that music is commonly composed of rhythm, harmony and melody. But if the drums play the rhythm, the guitar plays the harmony and the voice plays the melody, what does the bass do? Of course, the bass could play melodies and chords, but with neither of those being its primary function, what is the bass’ specific role instead?
The electric bass provides the harmonic and rhythmic base expressed in melodic form, playing the lowest note of a chord, multiple notes of a chord or even the full chord in its low register, plucking the notes one after the other (melodically, hence also using scale’s passing notes that are not part of the chords), giving, with a regular and specific rhythm, strength and structure to the piece.
In summary, a good bass player must be familiar with the chords and chord progressions at both the practical and theoretical level, and develop a solid harmonic, rhythmic and melodic awareness.